Dwarf Dinosaur Once Roamed Transylvania

The dwarf dinosaur, Magyarosaurus dacus, which lived in what is now Transylvania, was about the size of a horse and weighed some 230 pounds (103 kg). Its giant relatives could weigh up to 220,000 pounds (100,000 kg).Credit: Mihai Dumbrava, liliensternus.deviantart.com.

A relative of some of the largest dinosaurs to ever plod the
Earth never grew to be more than horse-size, confirming the beast was indeed a
dwarf dinosaur, a new study reveals.

The diminutive dino lived in what is now Transylvania,
Romania, some 75 million to 70 million years ago.

The remains of the dinosaur, named Magyarosaurus dacus, have been debated by scientists for years. Did
they belong to an actual dwarf dinosaur or a youngster that would later grow
into a hefty adult?

And M. dacus
belongs to a group of titanosaurs, which were giant sauropods (plant-eating
dinosaurs). Compared with one of the largest
titanosaurs, Argentinosaurus,
which ballooned to about the weight of 10 African elephants, this guy would've
been teensy.

Now, scientists have looked closely at the bone structure
from remains of the small dinosaur, finding clear evidence that the bones came
from fully grown individuals.

Bony history

The dinosaur's bones have a long history.

In 1895, the sister of an eccentric paleontologist Franz
Baron Nopcsa discovered small dinosaur bones on their family estate in
Transylvania. Around the same time another paleontologist had turned up dwarf
mammals, such as tiny elephants and hippopotamuses, on a Mediterranean island. Nopcsa
interpreted the dinosaur bones in the same vein, suggesting the remains
belonged to dwarf
dinosaurs.

Among these finds were a number of bones belonging to a
sauropod dinosaur which Nopcsa named Magyarosaurus
dacus, after his native country.

Later other sauropod bones were found, those belonging to
the giants of the titanosaur group. That led scientists to suggest the bones of
M. dacus were really just juveniles
and would have later grown to be enormous as adults.

Aging bones

To solve the mystery, Koen Stein of the Steinmann Institute
Division of Paleontology, University of Bonn, Germany, and his colleagues cut
up the bones from about 19 individuals of this species, collecting around 21
samples, which they looked at under a high-powered microscope. They were
looking for certain microstructures that have been found to change along the
life continuum of sauropod dinosaurs, from juveniles to mature individuals to
the seniors.

For one, the passages where blood vessels flow change with
time, becoming filled in with bone material. In addition, a process called
remodeling occurs in which the old bone matrix gets broken down, forming tiny
holes in the bone that get filled in with new bone matrix.

For humans this remodeling process starts in the teen years,
Stein said. "In humans by the time you're 25 the complete skeleton has
been completely resorbed and re-deposited again," Stein told LiveScience.

For M. dacus'
bones, they found the remains belonged to animals that were between 95 and 99
percent of their maximum size.

"We were able to prove that by looking at the
microstructure of the bone that they weren't juvenile," Stein said.

Island dwarfs

The dwarf body size was probably a result of environmental
factors found on the island where the dinosaur is thought to have lived. During
the Cretaceous period (from about 144 million to 65 million years ago), Transylvania is thought to
have been a small island in the Tethys Ocean, which has now become the Mediterranean
Sea.

In general,
animals get big to avoid large predators, and so when large predators aren't
around there's no need to waste energy growing to a large size, the thinking
goes. Islands often lack such big beasts.

There is no record of any oversized predators on the island
that's now connected to the mainland, Stein said.

Island environments also generally support only limited
resources.

"To sustain a healthy population of individuals you
need enough food," Stein said. "And if there's a limitation on food
the biggest individual with big food requirements will just starve."

And so keeping a petite figure is all about survival in the animal kingdom.

The results are now published in the journal Proceedings of the
National Academy of Sciences.

Jeanna Bryner

Before becoming managing editor, Jeanna served as a reporter for Live Science and SPACE.com for about three years. Previously she was an assistant editor at Scholastic's Science World magazine. Jeanna has an English degree from Salisbury University, a Master's degree in biogeochemistry and environmental sciences from the University of Maryland, and a science journalism degree from New York University.